I agree that instating UBI may become an excellent strategy for existing power structures to preserve themselves by paying out the minimal amount to prevent social unrest.

However, I think it will be nearly impossible to succeed in spinning it is "no strings attached" unless everyone really can continue to exercise all of their current rights (to free speech, to the democratic process, etc) without losing the benefits.

You make it sound like the state will be able to say "Don't speak in opposition to our policies or we'll let you starve". I'm skeptical.